The present invention relates to circuitry forming substrates used in a variety of electronic equipment and a manufacturing method of such circuitry forming substrates.
In recent years, as electronic equipment is seeing the ever-increasing level of size reduction and circuit density, a shift from conventional one surfaced substrates to two-surfaced substrates and multilayer substrates has been taking place in the area of circuitry forming substrates for mounting electronic components thereon, resulting in stepped up development of a high density circuitry forming substrate that enables the mounting of as many circuits as possible thereon.
With a high density circuitry forming substrate, in place of the conventional method of drilling to bore a hole (through hole) on a substrate, it is being considered to use energy beams such as a laser beam and the like, whereby machining at a higher speed and with a higher degree of definition is made possible. (cf. An article titled xe2x80x9cRemarkable Recent Trend in Development of Build-up Multilayer PWBxe2x80x9d authored by K. Takagi and appeared in xe2x80x9cSurface Mounting Technologyxe2x80x9d published in January, 1997 from Nikkan Kogyo Shinbun of Japan)
However, with a high density substrate, as the line width and land size of circuits are reduced, the adhesion strength between the substrate and the circuits or the lands is naturally reduced. On the other hand, a high density substrate is usually used in such electronic devices as note PC""s, portable telephones, PDA""s and the like, and is liable to suffering from such mechanical stresses as caused by dropping, bending, impacting and the like occurring on the part of the electronic devices. As a result, the aforementioned reduction in adhesion strength of the high density substrate has been making a serious problem.
As the substrate material for a high density substrate, most of the time, a resin material is used and a high grade thermosetting resin is usually used from the view points of enhancement in the mechanical strength or heat resistance of the substrate. Although the properties of the substrate itself may be improved, however, the adhesion strength between the substrate and the circuits or the lands is not necessarily intensified when such mechanical stresses as an impact and the like imposed on the substrate are taken into consideration.
Conversely, when a material design and a material selection are carried out for the whole purpose of increasing the adhesion strength, the substrate properties except for the adhesion strength are often degraded. Therefore, it is actually difficult for the substrate material development to be performed so as to satisfy all the requirements involved with a high density substrate.
In addition, with a high density circuitry forming substrate, such connecting means as a conductive paste, a metal plating and the like are used in electrically connecting between layers of the substrate and, on the other hand, a spacing between through holes or non-through holes, which are generally referred to as via holes and formed on the substrate for interlayer connections, and a spacing between the via hole and the adjoining wiring are made smaller and smaller, resulting sometimes in such a serious problem of reliability for the circuitry forming substrate as caused by diffusion of a conductive paste and a plating solution for metal plating to the vicinity of via holes.
A manufacturing method of circuitry forming substrates of the present invention comprises the steps of:
forming through holes or non-through holes on a plate-like or sheet-like substrate formed of a single material or a plurality of materials by irradiating an energy beam on the substrate;
forming a connecting means in the through hole or non-through hole formed in the foregoing hole forming step to connect electrically between the upper surface and the lower surface of the substrate or between the outer layer and the inner layer of the substrate; and
forming a circuit on the surface of the substrate by disposing a conductive layer formed of a metal foil or a thin film on the surface and patterning the cconductive layer to a desired configuration,
in which the foregoing each respective step is performed independently or the elements of each respective step are intermingled with one another for the purpose of achieving what is intended for by the foregoing respective steps, and further comprises the steps of;
attaching by adhesion a film-like separation film on a surface or both surfaces of the substrate before the foregoing step of forming holes, and having part of the separation film transferred onto the substrate.
According to the present invention, a thin foreign material is disposed on the upper surface of a substrate by a transferring method, thereby allowing the adhesion strength of the substrate to be intensified owing to the effect of the foreign material and also enabling the use of an optimum material as the substrate material that makes it possible for the substrate to achieve desired overall characteristics. More specifically, a material, which is different from the substrate material and yet intensifies the adhesion strength of the substrate, is selectively transferred onto the surface of the substrate only in an area where a circuit or a land is disposed, thus allowing a high density and high reliability circuitry forming substrate to be realized without degrading the overall characteristics of the substrate.
In addition, the manufacturing method of circuitry forming substrates comprises the steps of:
forming through holes or non-through holes on a plate-like or sheet-like substrate formed of a single material or a plurality of materials by irradiating an energy beam on the substrate;
forming a connecting means in the through hole or non-through hole formed in the foregoing hole forming step to connect electrically between the upper surface and the lower surface of the substrate or between the outer layer and the inner layer of the substrate; and
forming a circuit on the surface of the substrate by disposing a conductive layer formed of a metal foil or a thin film on the surface and patterning the conductive layer to a desired configuration,
in which the foregoing each respective step is performed independently or the elements of each respective step are intermingled with one another for the purpose of achieving what is intended for by the foregoing respective steps, and further comprises the steps of;
attaching by adhesion a film-like separation film on a surface or both surfaces of the substrate before the foregoing step of forming holes, making the substrate and separation film almost in one-piece construction in the foregoing film attaching step, and then making the one-piece construction into a more solid one-piece structure intensely in the periphery of the through holes or non-through holes in the foregoing step of forming holes with a resulting prevention of the diffusion of connecting means to around the via holes. As a result, it is made possible for a high density and high reliability circuitry forming substrate to be realized.
A manufacturing method of circuitry forming substrates in a first aspect of the present invention comprises the steps of:
forming through holes or non-through holes on a plate-like or sheet-like substrate formed of a single material or a plurality of materials by irradiating an energy beam on the substrate;
forming a connecting means in the through hole or non-through hole formed in the foregoing hole forming step to connect electrically between the upper surface and the lower surface of the substrate or between the outer layer and the inner layer of the substrate; and
forming a circuit on the surface of the substrate by disposing a conductive layer formed of a metal foil or a thin film on the surface and patterning the conductive layer to a desired configuration,
in which the foregoing each respective step is performed independently or the elements of each respective step are intermingled with one another for the purpose of achieving what is intended for by the foregoing respective steps, and further comprises the steps of;
attaching by adhesion a film-like separation film on a surface or both surfaces of the substrate before the foregoing step of forming holes, and
having part of the separation film transferred onto the substrate, thereby achieving the effects of increasing the adhesion strength between the substrate and the metal foil or the thin film from about 0.9 kg/cm of a traditionally normal value to about 1.2 kg/cm and the like in a strength test of peeling off a copper foil of 35 xcexcm thick and 1 cm wide from the substrate.
A manufacturing method of circuitry forming substrates in a second aspect of the present invention comprises the steps of:
forming through holes or non-through holes on a plate-like or sheet-like substrate formed of a single material or a plurality of materials by irradiating an energy beam on the substrate;
forming a connecting means in the through hole or non-through hole formed in the foregoing step of forming holes to connect electrically between the upper surface and the lower surface of the substrate or between the outer layer and the inner layer of the substrate; and
forming a circuit on the surface of the substrate by disposing a conductive layer formed of a metal foil or a thin film on the surface and patterning the conductive layer to a desired configuration,
in which the foregoing each respective step is performed independently or the elements of each respective step are intermingled with one another for the purpose of achieving what is intended for by the foregoing respective steps, and further comprises the steps of;
attaching by adhesion a film-like separation film on a surface or both surfaces of the substrate before the foregoing step of forming holes, making the substrate and separation film almost in one-piece construction in the foregoing film attaching step and then making the one-piece construction into a more solid one-piece structure intensely in the periphery of the through holes or non-through holes in the foregoing step of forming holes with a resulting effect of preventing the diffusion of connecting means such as a conductive paste and the like used in the connecting means forming step to around the holes and the like.
A manufacturing method of circuitry forming substrates in a third aspect of the present invention comprises the steps of:
forming through holes or non-through holes on a plate-like or sheet-like substrate formed of a single material or a plurality of materials by irradiating an energy beam on the substrate;
forming a connecting means in the through hole or non-through hole formed in the foregoing hole forming step to connect electrically between the upper surface and the lower surface of the substrate or between the outer layer and the inner layer of the substrate; and
forming a circuit on the surface of the substrate by disposing a conductive layer formed of a metal foil or a thin film on the surface and patterning the conductive layer to a desired configuration,
in which the foregoing each respective step is performed independently or the elements of each respective step are intermingled with one another for the purpose of achieving what is intended for by the foregoing respective steps, and further comprises the steps of;
attaching by adhesion a film-like separation film on both surfaces of the substrate before the foregoing step of forming holes, and
having the separation film near a perimeter or in a periphery of the through hole or non-through hole made to an elevated area which is formed of the separation film or mainly of the separation film with the substrate included and located at both sides or one side of an outside and a substrate side of the separation film by thermal effect in the hole forming step, so as to make a thickness of the elevated area larger at an energy beam incident side than at an energy beam releasing side resulting in such effects as exercising beneficial features of the elevated area at the side where the energy beam is incident and the like.
A manufacturing method of circuitry forming substrates in a fourth aspect of the present invention is the same as the manufacturing method of circuitry forming substrates in the first aspect of the present invention except for having part of the separation film transferred to near the periphery of the through hole or non-through hole formed in the hole forming step, resulting in such effects as intensifying the strength of adhesion between a circuit around a hole, i.e., a land and the substrate, and the like.
A manufacturing method of circuitry forming substrates in a fifth aspect of the present invention is the same as the manufacturing method of circuitry forming substrates in the first aspect of the present invention except for having part of the separation film transferred by irradiating an energy beam on the entire area or part of the area where a circuit formed in the circuit forming step, resulting in such effects as intensifying the strength of adhesion between the circuit and the substrate, and the like.
A manufacturing method of circuitry forming substrates in a sixth aspect of the present invention is the same as the manufacturing method of circuitry forming substrates in the first aspect or the second aspect except for using a porous base material that contains voids as the substrate material and also having a layer, which is free of voids or scarce of voids, formed of a material for separation films or a material prepared by mixing the substrate material and the material for separation films and disposed around the through hole or non-through hole formed in the hole forming step, thereby allowing the strength in adhesion between the land and the substrate to be intensified and also enabling the achievement of the effect of preventing a short circuit and the like caused by a conductive paste diffusing to around the holes.
A manufacturing method of circuitry forming substrates in a seventh aspect of the present invention is the same as the manufacturing method of circuitry forming substrates in the first aspect, the second aspect or the third aspect,
in which the step of forming a connecting means further comprises a step of filling a conductive paste in the through holes or non-through holes that are formed in the step of forming holes, and then the separation film is peeled off from the substrate, a metal foil or a circuitry forming substrate for inner layer is disposed on one surface or both surfaces of the substrate, respectively, and a pressing force is applied thereto while heat being applied, thereby achieving the integration into a one-piece structure of the substrate and the metal foil or the substrate and the circuitry forming substrate for inner layer and realizing an electrical connection between the upper and lower surfaces or the outer and inner layers of the substrate by the use of a conductive paste with the step of forming circuitry with a patterning process applied to the metal foil following thereafter. Accordingly, there are provided such effects as maintaining a sufficient filling amount of the conductive paste and the like by making the swelling larger at the side of the surface thereof where the conductive paste is less liable to being taken away with the separation film when the separation film is peeled off from the substrate.
A manufacturing method of circuitry forming substrates in an eighth aspect of the present invention is the same as the manufacturing method of circuitry forming substrates in the first aspect, the second aspect or the third aspect,
in which the separation film is peeled off from the substrate after the step of forming holes, a metal foil or a circuitry forming substrate for inner layer is disposed on one surface or both surfaces of the substrate, respectively, and a pressing force is applied thereto while heat being applied, thereby achieving the integration into a one-piece structure of the substrate and the metal foil or the substrate and the circuitry forming substrate for inner layer, and then an electrical connection between the upper and lower surfaces or the outer and inner layers of the substrate is realized by forming a thin film inside of the holes and entirely or partly on one surface or both surfaces of the substrate by means of a plating method, a deposition method or some other thin film forming methods with the step of the forming circuitry by applying a patterning process to the thin film following thereafter. Accordingly, there are provided such effects as maintaining a sufficient strength in adhesion between the plating or thin film and the substrate, preventing the infiltration of a plating solution and the like.
A manufacturing method of circuitry forming substrates in a ninth aspect of the present invention is the same as the manufacturing method of circuitry forming substrates in the first aspect, the second aspect or the third aspect,
in which the separation film further comprises a base film with a single coating layer or a plurality of coating layers disposed on one surface or both surfaces thereof and the one coating layer or the plurality of coating layers are transferred onto, integrated with or made to form a swelling on the substrate by being taken from the separation film in the hole forming step and circuit forming step, resulting in such effects as making a selection of materials to be transferred onto the substrate in such a way that the strength of adhesion is intensified, providing freedom of choice against the numerous requirements regarding the machinability and the like in the step of forming holes, and the like.
A manufacturing method of circuitry forming substrates in a tenth aspect of the present invention is the same as the manufacturing method of circuitry forming substrates in the ninth aspect,
in which the coating layer to be transferred onto the substrate from the separation film is formed of a thermoplastic resin or a thermoplastic material prepared by having a thermosetting resin mixed with a thermoplastic resin, resulting in such effects as intensifying the strength in adhesion between the circuit and the substrate and the like due to the flexibility realized by a thermoplastic resin.
A manufacturing method of circuitry forming substrates in an eleventh aspect of the present invention is the same as the manufacturing method of circuitry forming substrates in the ninth aspect,
in which the coating layer to be transferred onto the substrate from the separation film is formed of a thermosetting resin or a thermoplastic resin mixed with a thermosetting resin having heat curing and heat resistance, resulting in such effects as enhancing the strength in adhesion and heat resistance between the circuit or land and the substrate, and the like because of the use of a thermosetting resin. For example, with a circuitry forming substrate produced according to the manufacturing method of circuitry forming substrates in the ninth aspect of the present invention by the use of a separation film prepared by applying about 1 xcexcm thickness composite of 79 parts by weight of epoxy denatured polyurethane, 10 parts by weight of bisphenol A type epoxy resin and 10 parts by weight of novolak type phenol resin as a curing agent and 1 part by weight of imidazole as a curing accelerator, to both surfaces of a 20 xcexcm thick base film mainly formed of polyethylene phthalate, and then dried and cured, the adhesion strength under a high temperature is improved to about 1.0 kg/cm in comparison with the normal adhesion strength of 0.5 kg/cm of a prior art circuitry forming substrate in a strength test of peeling off a copper foil measuring 1 cm in width and 35 xcexcm in thickness from a substrate heated to 150xc2x0 C. in temperature.
A manufacturing method of circuitry forming substrates in a twelfth aspect of the present invention is the same as the manufacturing method of circuitry forming substrates in the ninth aspect,
in which the coating layer transferred to the substrate from the separation film is formed of a metallic thin film, resulting in such effects as preventing corrosion or migration of metallic materials used in the circuit or land, and the like.
A manufacturing method of circuitry forming substrates in a thirteenth aspect of the present invention is the same as the manufacturing method of circuitry forming substrates in the first aspect, the second aspect or the third aspect, except for having a surface roughening treatment applied to one surface or both surfaces of the metal foil, resulting in such effects as allowing the adhesion strength to be intensified more efficiently and the like because of the interaction between the asperities produced by the surface roughening treatment and the material transferred.
A manufacturing method of circuitry forming substrates in a fourteenth aspect of the present invention is the same as the manufacturing method of circuitry forming substrates in the thirteenth aspect except for making the average extent of the surface roughness produced by the surface roughening treatment larger than the thickness of part of the separation film transferred onto the substrate, resulting in such effects as intensifying both the static adhesion strength and the dynamic adhesion strength that is needed to withstand a mechanical shock encountered in a drop test, for example, and the like because the peaks of the roughened surface pierce through part of the transferred separation film to get to the substrate, thereby allowing the metal foil to be joined with both substrate and separation film and the respective features in physical property of the substrate material and separation film to be exploited.
A manufacturing method of circuitry forming substrates in a fifteenth aspect of the present invention is the same as the manufacturing method of circuitry forming substrates in the thirteenth aspect except for making the average extent of the surface roughness produced by the surface roughening treatment smaller than the thickness of part of the separation film transferred onto the substrate, resulting in such effects as allowing the material transferred to act more efficiently as a cushion and the like because there is no direct contact between the substrate and the metal foil and also to act as a protector and the like to shield the metal foil from the substrate in case a material corrosive to the metal foil is contained in the composition of the substrate material.
A manufacturing method of circuitry forming substrates in a sixteenth aspect of the present invention is the same as the manufacturing method of circuitry forming substrates in the first aspect, in the second aspect or in the third aspect except for using a laser beam as the energy beam for the step of forming holes, resulting in such effects as facilitating the control of energy for machining and the like so as to achieve the intended objectives such as transferring and the like efficiently.
A manufacturing method of circuitry forming substrates in a seventeenth aspect of the present invention is the same as the manufacturing method of circuitry forming substrates in the sixteenth aspect except for using a carbon dioxide laser beam as the energy beam for the step of forming holes, resulting in such effects as a reduction in cost of forming holes by laser beam machining, excellent machinability in forming holes on a resin material, and the like
A manufacturing method of circuitry forming substrates in an eighteenth aspect of the present invention is the same as the manufacturing method of circuitry forming substrates in the sixteenth aspect,
in which the wavelength of the laser beam is shorter than 10 xcexcm and longer than 9 xcexcm, resulting in such effects as bringing benefits to transferring, forming of a one-piece structure or shaping of a suitable swelling, and the like.
A manufacturing method of circuitry forming substrates in a ninteenth aspect of the present invention is the same as the manufacturing method of circuitry forming substrates in the sixteenth aspect,
in which the laser beam is irradiated one time or a plurality of times in a pulse shape with the pulse energy for at least the first time of the laser beam irradiation exceeding 10 mJ, resulting in such effects as bringing benefits to transferring, forming of a one-piece structure or shaping of a suitable swelling, and the like.
A manufacturing method of circuitry forming substrates in a twentieth aspect of the present invention is the same as the manufacturing method of circuitry forming substrates in the first aspect, the second aspect or the third aspect,
in which a B-stage resin prepared by having a reinforced material impregnated with a thermosetting resin, i.e., what is called a prepreg or a film prepared by making a B-stage resin from a thermosetting resin without using a reinforced material is used as the substrate, resulting in such effects as facilitating the substrate material and separation film to be formed into a one-piece structure, and the like.
A manufacturing method of circuitry forming substrates in a twenty first aspect of the present invention is the same as the manufacturing method of circuitry forming substrates in the first aspect,
in which part of the separation film transferred onto the substrate is 3 xcexcm or less in thickness, resulting in such effects as allowing a circuitry forming substrate to be manufactured without losing the properties of the substrate material and the like.
A manufacturing method of circuitry forming substrates in a twenty second aspect of the present invention is the same as the manufacturing method of circuitry forming substrates in the first aspect or the second aspect, in which any surface out of both surfaces of the substrate, where transferring of the separation film or forming of a layer free of voids is performed efficiently, is arranged to be located on the upper layer side of the circuitry forming substrate, resulting in such effects as making the transferring and forming of a one-piece structure contribute to working effectively on the upper most part of the substrate where the strength in adhesion between the circuit and the substrate is considered as important.
A circuitry forming substrate in a twenty third aspect of the present invention has a material structure,
in which the thermoplasticity of a place inside the substrate decreases stepwise as the distance of the place from the circuit or land formed on the upper surface of the substrate increases in the thickness direction of the substrate starting from immediately below the upper surface of the substrate, thereby allowing the substrate employing a thermosetting material as the main material thereof to achieve such an effect as realizing the required characteristics in stiffness, mechanical strength and the like while maintaining the adhesion strength of the circuit or land by providing the substrate immediately below the circuit or land with thermoplasticity, i.e., flexibility.